Description of problem: Video showing the problem: http://oirase.annexia.org/tmp/20160505_151205.mp4 When connected to an external 4K monitor over HDMI, recent kernels show uncontrollable flickering. Hardware: - Lenovo T450s - Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz - Intel(R) HD Graphics 5500 Ubuntu are tracking a similar bug here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1554613 However if I understand their solution correctly, which was to try the drm-intel-next kernel, that did NOT work for me. I added drm-intel-next-2016-04-25 to our kernel, but that did not fix it. Version-Release number of selected component (if applicable): kernel-4.3.3-301.fc23 => works OK kernel-4.4.4-301.fc23 => fails kernel-4.5.2-302.fc24 => fails kernel-4.6.0-0.rc6.git2.1.fc25 => fails kernel-4.6.0-0.rc6.git2.1.fc25 + drm-intel-next-2016-04-25 => fails How reproducible: 100% Steps to Reproduce: 1. Plug in external monitor 2. Select a high resolution, eg. 3K or 4K 3. Flickering.
Created attachment 1154234 [details] dmesg dmesg says that I should try increasing the memory steal in the BIOS, but it is already set to the maximum.
Created attachment 1154236 [details] journal from boot
A bit more testing of different versions: kernel-4.3.3-301.fc23 => worked before, now fails kernel-4.4.4-301.fc23 => failed before, now works kernel-4.5.0-0.rc7.git0.2.fc24 => fails kernel-4.5.2-302.fc24 => fails kernel-4.6.0-0.rc6.git2.1.fc25 => fails kernel-4.6.0-0.rc6.git2.1.fc25 + drm-intel-next-2016-04-25 => fails
This bug appears to have been reported against 'rawhide' during the Fedora 25 development cycle. Changing version to '25'.
Upgrading to 4.8.7-300.fc25.x86_64 seems to have fixed this.